1. Field of the Invention
This invention relates to the production of a foamed material as a continuous, unsupported profile. More particularly, this invention relates to the production of continuous low density foam profiles by extruding a liquid foamable composition around a continuous filament as a core.
2. Background Information
Methods for applying relatively thin coatings of liquid materials on to filamentary structures such as fibers and wires are well known, as are methods for coating filamentary structures with thermoplastic materials that are solid at 25.degree. C.
It is known to extrude a small diameter stream of foamable organic or organosiloxane polymer compositions on to a substrate to form a gasket, however the composition cannot support its own weight until at least the surface of the extruded article is crosslinked.
The extrusion of a layer of foamed polyethylene with a thickness of up to 1 mm using molten polymer as the coating material is described in Japanese Laid Open Patent Application No. 50/47247.
Extrusion of a melt-extrudable resin, a foaming agent and a foaming aid is described in Japanese Patent No. 1,149,839 and 1,149,840. The process can be used to form a foam coating on a wire.
Extrusion of foam-coated wire by blending a resin with a solvent type foaming agent at a concentration of 0.1 to 10 parts by weight per 100 parts of resin and extruding the resultant mixture around a copper wire is described in Japanese Laid Open Patent Application No. 57/84,828. A similar process using polyethylene in combination with a chemical blowing agent is described in Japanese Laid Open Patent Application 57/84,517.
The addition of 30 to 120 weight percent, based on the weight of polymer, of a liquid foaming agent into a molten polymer within an extruder is described in British Patent Application 1,410,979. The action of the foaming agent is suppressed until the blend of polymer and foaming agent exits from the extruder.
Extrusion of a mixture of molten polypropylene, a foaming agent and a crosslinking agent onto a wire is described in German Patent Application 1,504,355 A.
A method for manufacturing a foamed part containing reinforcement core wires embedded therein is described in Japanese Laid Open Patent Application 63/230,316.
Extrusion of a 5-50 weight percent solution of a high molecular weight polyolefin through an annular gap around the object to be coated followed by stretching of the extrudate is described in European Laid Open Application No. 281,209 A. The solvent is substantially removed from the extrudate during stretching.
In the past it has not been feasible to continuously extrude at ambient temperature self-supporting profiles using crosslinkable, foamable compositions that are liquid at 25.degree. C. and cure to yield foams with a density lower than about 30 lb/ft.sup.3 (480 kg/m.sup.3).
Foam prepared by extruding molten or solubilized non-curable polymer compositions containing a heat-activated blowing agent typically exhibit higher compression deflection values (greater force required for a given percent compression), higher densities and higher compression set values than foams prepared from curable compositions that are liquid under ambient conditions.
One objective of this invention is to provide a method for extruding foams using curable compositions that are flowable under ambient conditions. A second objective is to provide soft, compressible foams exhibiting a relatively uniform cell structure as continuous self-supporting profiles.